We are requesting support for a 4th International Symposium on Oxidases and Related Redox Systems. Many books and symposia have recently treated restricted phases of the overall problem of structure/function in dioxygen enzymology but none has sought to define the principles which govern the functions of these proteins in general, considering all types of oxygen-active catalytic sites comparatively and at several levels of biological organization, as we now propose to do. Fifty specialized authorities will be convened to compare among these proteins: (a) the mechanisms of electron, proton, and hydride ion transfer among the proteins, substrates, cofactors, and active sites, in solution and across membranes, (b) the structural states of dioxygen in relevant aqueous and hydrophobic environments, (c) structure as a composite of results from contemporary technical probes especially X-ray crystallography, (d) mechanisms, (e) the molecular biology of oxidases, oxygenases, and oxygen-transporting proteins with respect to gene structure and sequence of the component domains, (f) mechanisms of adaptation of these proteins, and (g) their evolution in the light of various contemporary theories of evolutionary mechanisms, particularly intervention of mobile genetic elements and interspecific transfer of elements as well as more conventional processes for the generation of diversity, and (h) the mechanism and evolution of photosynthetic O2 generation. We also wish to explore certain physiological problems: the existence or not of O2 concentration gradients within cells and the nature of signals that regulate the concentration and activity of oxygen-interactive enzymes.